1. Field of the Invention
The present invention relates to intake devices for internal combustion engines, and more particularly, an intake device that controls an intake flow passing through an intake pipe to thus improve the combustion efficiency of the internal combustion engine.
2. Description of the Related Art
There are various proposals of an intake device that controls an intake flow by an open/close valve arranged in an intake pipe (also called intake port) through which the intake air is supplied to the cylinder side of the internal combustion engine. For example, Japanese Patent Application Publication No. 2004-124836 discloses the use of a partition plate (wall) arranged in an intake passage along a longitudinal direction thereof so that the intake passage is divided into first and second passages respectively located on the upper and lower sides of the partition plate. Further, two plate-shaped valve plates that rotate about a supporting shaft are arranged on the upstream side of the partition plate, and are capable of opening and closing a part of the intake passage. It is thus possible to adjust the opening ratio of the intake passage and reinforce a tumble flow, so that stable combustion of a lean air-fuel mixture can be achieved.
However, the use of the two valves rotating about the single shaft results in a complex mechanical structure. Further, one of the two valves arranged to the first passage for forming the tumble flow is comparatively small, and has a difficulty in forming a desired strong tumble flow.